Add few methods to allow peers to exchange authentication information.
- `set_auth_callback(callback)`: Enable the authentication features.
The callback is a `Callable` that accepts an `int` (the peer ID), and
a `PackedByteArray` of data.
- The `peer_authenticating(id)` signal will be emitted instead of
`peer_connected` when a new peer connects.
- Use `send_auth(id: int, data: PackedByteArray)` to exchange data.
- Call `complete_auth(id: int)` when the authentication process is
complete and you expect to start receiving game data.
- The `peer_connected` signal will be emitted as soon as both parties
complete the authentication.
- Use `disconnect_peer(id)` to disconnect a connected peer.
- If the `peer_connected` signal didn't fire for that peer (i.e. it was
still in the authentication phase), the `peer_auth_failed` signal will
be emitted instead of `peer_disconnected`.
MultiplayerPeer changes:
- Adds is_server_relay_supported virtual method
Informs the upper MultiplayerAPI layer if it can signal peers connected
to the server to other clients, and perform packet relaying among them.
- Adds get_packet_channel and get_packet_mode virtual methods
Allows the MultiplayerAPI to retrieve the channel and transfer modes to
use when relaying the last received packet.
SceneMultiplayerPeer changes:
- Implement peer signaling and packet relaying when the MultiplayerPeer
advertise they are supported.
ENet, WebRTC, WebSocket changes:
- Removed custom code for relaying from WebSocket and ENet, and let it
be handled by the upper layer.
- Update WebRTC to split create_client, create_server, and create_mesh,
with the latter behaving like the old initialize with
"server_compatibility = false", and the first two supporting the upper
layer relaying protocol.
- RPC configurations are now dictionaries.
- Script.get_rpc_methods renamed to Script.get_rpc_config.
- Node.rpc[_id] and Callable.rpc now return an Error.
- Refactor MultiplayerAPI to allow extension.
- New MultiplayerAPI.rpc method with Array argument (for scripts).
- Move the default MultiplayerAPI implementation to a module.
